The present invention relates generally to internal combustion engines, and more particularly, to a system and method of detecting spark plug fouling and switching an operation mode of the internal combustion engine to correct any spark plug fouling that is detected.
In general, fuel-injected engines include a fuel injector that provides a fine mist of fuel that mixes with combustion generating gases, that generally comprise a mixture of fresh air and any remaining exhaust gases. Ideally, this mixture is compressed and spark ignited. The spark ignition is typically provided by a spark plug. The spark plug is essentially a pair of electrodes disposed within a combustion chamber and separated by an air gap. One spark plug electrode is connected to an intermittent voltage potential and the other is connected to an electrical ground. When a sufficient voltage potential is present at one electrode, a spark occurs across the air gap.
Certain fuel-injected internal combustion engines have been refined to operate in two combustion modes that can be defined as a stratified operation and a homogenous operation. When the engine is operating at low speeds and/or loads, a stratified operation is generally preferred, wherein fuel is introduced into the combustion chamber and spark ignited on injection. In contrast, when the engine is operating at higher engine speeds and/or loads, a homogenous operation is preferred, wherein fuel is allowed to hit the piston and intermix more thoroughly with the combustion gases before ignition. Therefore, the homogenous combustion mode is characterized by a generally uniform and relatively rich fuel charge in the combustion chamber. On the other hand, a stratified operating mode is characterized by fluctuations in the fuel and gas mix, or equivalence ratio. Engines that operate in homogeneous and stratified modes must be calibrated to switch between cylinders either individually or all at once from stratified to homogeneous when transitioning to higher speeds and from homogeneous to stratified when transitioning from high speed to low speed. The present invention is particularly applicable in engines that transition cylinders individually. However, it is contemplated that the present invention is also applicable in systems that transition all cylinders together.
Stratified combustion can include an air/fuel mixture having mainly a lean mixture about a periphery of the combustion chamber surrounding a relatively small layer or pocket of rich mixture near a center of the combustion chamber. In one mode, the rich mixture is initially ignited by firing a spark into the combustion chamber early in the combustion cycle wherein the ignition spreads to the leaner mixture consuming the rest of the leaner mixture in the combustion chamber. Therefore, unlike operating under homogeneous condition, when operating under stratified conditions, the spark plug fires while the injected fuel has yet to reach the piston and evenly disperse. As such, when operating the engine in a stratified operation mode, soot can develop in the combustion chamber from the direct ignition of unvaporized fuel.
Additionally, other operating modes are also known to cause soot production in the combustion chamber. For example, if the engine is operating in an incorrect heat range or operating with an incorrect air/fuel mixture, soot may also be formed within the combustion chamber.
Over time, the buildup of soot deposited on the electrodes of the spark plug can interfere with the spark across the electrodes. That is, rather than causing a clean, well defined spark across the air gap, the voltage potential can be discharged, or partially dissipated, via the soot buildup. This buildup of soot, known as spark plug fouling, can cause the engine to misfire. The result is a loss of power provided by the engine.
The detection of spark plug fouling generally requires an inspection of the spark plug. Such an inspection requires that engine operation cease and the spark plugs be removed. Furthermore, to correct spark plug fouling, the spark plugs must be manually cleaned or replaced. The operating parameters of the engine must then be augmented incrementally until spark plug fouling ceases.
Such an inspection and correction process not only requires that the engine be taken out of operation, but with the advanced nature of current engines, may also require the mechanical proficiency of trained service personnel. It would therefore be desirable to have a system and method to automatically detect and correct spark plug fouling in a combustion engine while the engine is in operation.